1. Field of the Invention
The present invention relates to a method and apparatus for controlling a hard disc drive (HDD), and more particularly, to a seek control method of smoothly changing to a coast mode and a deceleration mode in a track-seek control device according to a multi-sinusoidal acceleration trajectory, a recording medium suitable for the same, and an HDD adopting the same.
2. Description of the Related Art
A hard disc drive (HDD) includes a plurality of magnetic transducers for writing and reading information by magnetizing a disc and sensing a magnetic field on the disc. The information is stored on concentric tracks. Each track has a unique disc number and track number. In a plurality of discs, tracks having the same track number are called a cylinder. Therefore, each track can be defined by number of the cylinder.
Each transducer is typically integrated in a slider assembled with a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The actuator arm has a voice coil, which is located adjacent to a magnetic assembly specifying (supporting) a voice coil motor (VCM) together. The HDD typically includes a driving circuit, which supplies a current for exciting the VCM, and a controller. The excited VCM rotates the actuator arm to move the transducers across surfaces of the discs.
When writing or reading the information, the HDD may perform a track-seek control routine for moving the transducer from one cylinder to another. During the track-seek control routine, the VCM is excited to move the transducer from a certain cylinder to a new cylinder. The controller controls the current for exciting the VCM to move the transducer exactly to a target cylinder and a center of the track.
It is preferable to minimize the time required to read or write information from or on discs. Therefore, the track-seek control routine performed by the HDD needs to move the transducer to a new cylinder position as quickly as possible. In addition, a settling time of the HGA should be minimized so that the transducers can write or read the information as quickly as possible.
In a conventional method, the track-seek control is performed to move the transducer to a target track using a square wave acceleration trajectory. Unfortunately, a square wave includes harmonic waves of high frequencies. These harmonic waves result in a mechanical resonance in a HGA and thereby cause mechanical components or assemblies to vibrate. In addition, residual vibration incurs audible noise. In addition, the mechanical resonance generated by the track-seek control method using the conventional square wave acceleration trajectory causes an increase of both of the settling time required to write or read information on or from discs and an entire seek time.
A technology developed to resolve this problem is a track-seek control method using a sinusoidal acceleration trajectory. A track-seek controller using the sinusoidal acceleration trajectory has advantages in terms of vibration and audible noise as compared with the track-seek control method using the square wave acceleration trajectory.
FIG. 1 is a block diagram of a conventional track-seek control apparatus 100 using a sinusoidal acceleration trajectory.
Referring to FIG. 1, the track-seek control apparatus 100 includes a sinusoidal trajectory generator 102, a notch filter 116, a VCM driver 126, a head/disc assembly (HDA) 128, and a state estimator 104.
The track-seek control apparatus 100 performs a track-seek control routine for moving a transducer from a track to a target track located at a distance of a track-seek distance KSK.
The sinusoidal trajectory generator 102 generates a position y*(k), a velocity v*(k), and an acceleration a*(k) based on the sinusoidal acceleration trajectory at every sampling period TS.
In order to obtain values of sine and cosine functions to generate the sinusoidal acceleration trajectory, the sinusoidal trajectory generator 102 can sample the values of sine and cosine functions according to the sampling period TS, store the sampled values in a ROM table (not shown), and read the stored values in reference to the sampling period TS.
The ROM table stores the values of sine and cosine functions at a first sampling period with respect to a plurality of representative frequencies. The values of sine and cosine functions at the first sampling period with respect to a frequency between the representative frequencies are determined by interpolation. Here, the frequency corresponds to a track-seek distance and a seek time. That is, if the track-seek distance is determined, the seek time, i.e., the frequency of a sinusoidal signal, is determined based on the determined track-seek distance.
FIG. 2 is a diagram illustrating normalization of a position trajectory y, a velocity trajectory v, and an acceleration trajectory a in a conventional sinusoidal seek. Here, a time axis is normalized with respect to a track-seek time TSK. That is, FIG. 2 shows the position trajectory y, the velocity trajectory v, and the acceleration trajectory a when the track-seek time TSK is 1.
Referring to FIG. 2, the track-seek time TSK corresponds to one period of the sinusoidal acceleration trajectory a. Also, a transducer is moved to the track-seek distance KSK for the track-seek time TSK by controlling the transducer to have the sinusoidal acceleration trajectory a.
The state estimator 104 outputs an estimated position y(k) and estimated velocity v(k) of the transducer based on positions at previous samples k-1, k-2, . . . and a position at a current sample k of the transducer.
A track position, i.e., a track number, is obtained by a gray code recorded in a sector area of a disc, and the transducer reads the gray code while moving on the disc. The gray code read by the transducer is input to the state estimator 104.
The track-seek control apparatus 100 using a sinusoidal acceleration trajectory shown in FIG. 1 improves the settling time and reduces the audible noise generated by the square wave seek control method. However, in the sinusoidal seek control method, the seek time is increased around 10% as compared with the square wave seek control method. The reason can be understood by comparing a sine wave with a square wave. An occupying area of the sine wave is smaller than that of the square wave, which has the same amplitude each other, in one period. Each of the occupying areas is corresponding to an amount of current to accelerate and decelerate a VCM motor. Since the amount of current to accelerate or decelerate the VCM motor is smaller in the sinusoidal seek control method than in the square wave seek control method, the amount of driving of the VCM motor is smaller. Meanwhile the seek time is longer in the sinusoidal seek control method than in the square wave seek control method.
A multi-sinusoidal seek control method has been developed to improve this disadvantage. The multi-sinusoidal seek control method is disclosed in Korean Patent Publication Nos. 2001-62386, which was filed on Jul. 7, 2001, and 2001-67380, which was filed on Jul. 12, 2001. While the sinusoidal seek control method uses one sine wave, the multi-sinusoidal seek control method uses a harmonic wave obtained by synthesizing at least two sine waves.
FIG. 3 is a diagram illustrating an acceleration trajectory used in the multi-sinusoidal seek control method. The acceleration trajectory is obtained by synthesizing a plurality of sine waves having different frequencies respectively. An accelerating duration is depicted of being symmetrical to a decelerating duration in FIG. 3. However, in most cases, the accelerating duration and the decelerating duration are asymmetrical. A main reason of the asymmetry is because multiple sinusoidal acceleration trajectories are synthesized. Besides, the reason is because the residual vibration of the mechanical components is reduced and a ratio of the accelerating duration to the decelerating duration is varied in order to reduce the settling time. This is obtained by varying a synthesizing ratio of the sine waves.
Typically, the seek control has an acceleration mode, a deceleration mode, and a coast mode in which an actuator is coasted at a maximum design speed for long distance seeking. In general, a maximum value of a current input to a VCM in the seek control is limited to a predetermined value in consideration of performance and mechanical vibration of the VCM. That is, in the acceleration mode, the maximum design speed of the actuator is limited to the maximum value of the current. Also, since an acceleration trajectory and a deceleration trajectory should be symmetrical if at all possible, the deceleration mode is performed after the actuator reaches the maximum velocity. Accordingly, a distance, which can be sought only with the acceleration mode and the deceleration mode, is limited. Therefore, the coast mode is necessary to seek a distance longer than a predetermined distance.
FIG. 4 is a diagram illustrating an acceleration trajectory for the seek control including the coast mode in the multi-sinusoidal seek control method. In the coast mode, a value of the current input to the VCM is 0. In detail, velocity of the actuator is accelerated by applying current on a VCM in the acceleration mode, and when the velocity of the actuator is maximum, i.e., at a position A of FIG. 4, the acceleration mode is changed to the coast mode by blocking the current input to the VCM. The actuator is not accelerated any more and is coasted at a maximum speed by inertia. After coasting for a predetermined distance, the coast mode is changed to the deceleration mode at a position B. In the deceleration mode, the velocity of the actuator is decelerated by applying opposite current on the VCM. Accordingly, the actuator stops on a target track. For accurate seek control, the change to the coast mode and the change to the deceleration mode should be accurately controlled. The accurate control is more important when considering that the actuator moves at the maximum speed in the coast mode.
However, as described in FIG. 3, it is difficult to perform the coast mode due to the asymmetry of the acceleration mode and the deceleration mode for a plurality of reasons. In other words, the time (A of FIG. 4) when the velocity of the actuator is maximum in the acceleration mode varies, and if the change to the coast mode and the change to the deceleration mode are not exactly performed in accordance with the times A and B, respectively, accurate seek control cannot be achieved.
Also, if the mode change times are not exactly matched to the times A and B, audible noise is generated due to vibration of the actuator, and in a severe case, the seek fails.
In the conventional sinusoidal seek control method, entering the coast mode is simply performed at the half of a maximum seek time corresponding to the case without the coast mode.
Accordingly, since the change to the coast mode and the change to the deceleration mode are not smoothly performed in a multi-sinusoidal seek, the seek fails, or a seek time is delayed.